Paper type identification apparatus and image forming apparatus

ABSTRACT

A paper type identification apparatus includes a passage configured to allow a sheet to be manually inserted thereinto, a reading sensor configured to read a surface of the sheet inserted into the passage and a controller configured to output a notification after reading a first surface of the sheet by the reading sensor. The notification is a notification to urge a user to read a second surface opposite to the first surface of the sheet by the reading sensor, and determine a type of the sheet based on a reading result of the first surface by the reading sensor and a reading result of the second surface by the reading sensor.

BACKGROUND OF THE INVENTION Field of the Invention

The present disclosure relates to a paper type identification apparatuswhich can identify a type of a sheet and an image forming apparatushaving the paper type identification apparatus.

Description of the Related Art

Electrophotographic image forming apparatuses such as a copying machine,a printer, a facsimile, and a multifunction apparatus, form an image ona sheet conveyed in a conveyance path by performing each process ofelectrification, exposure, development, transfer, and fixing. There arevarious types of the sheets which can be used for image forming. Thesheets differ in characteristics (physical properties), such as sheetthickness, a degree of smoothness, basis weight, and surface property,according to the type of the sheet. The optimal operation condition ineach process of image forming changes according to the physicalproperties of the sheet to be used. Therefore, the image formingapparatus needs to change the conditions of operations, such as anadjustment value of each process, based on the type of sheet. Upon usingthe image forming apparatus, a user registers the type of the sheet tobe used previously. However, in a case where the registered type of thesheet is incorrect, the image forming apparatus cannot form images underproper operating conditions. In this case, the normal image cannot beformed on the sheet. For example, abnormalities arise in the imageformed on a sheet due to occurrence of jam, poor fixing, and a poorimage density, etc.

Japanese Patent Application Laid-open No. 2020-123835 describes an imageforming apparatus which identifies a type of a sheet by a measurementdevice (media sensor) which measures a feature amount of the sheet toperform image forming. The measurement device notifies the image formingapparatus of the measurement result of the sheet. The image formingapparatus specifies a paper profile that matches the measurement result,among a plurality of previously stored paper profiles. Therefore, theincorrect setting of the type of sheet is suppressed.

In some measurement devices which measure the feature amount of thesheet manually inserted by a user, only one side of the sheet ismeasured. In this case, only the feature amount of one side of the sheetis measured. It is noted that feature amounts of front surfaces (printsurfaces) of the sheets are previously registered in the paper profile,and the image forming apparatus identifies the paper type by reading thefront surface of the sheet when measuring the sheet by the measurementdevice. However, as to a sheet (for example, a recycled paper sheet) inwhich the feature amount of a front surface and that of a back surfacediffer from each other and the appearance of the front surface and theback surface is the same, there may be an increased risk of mistakenlymeasuring the front and back surfaces. The difference in the featureamount of the front surface and the back surface may cause incorrectdetection of the paper type.

SUMMARY OF THE INVENTION

A paper type identification apparatus according to one aspect of thepresent disclosure includes: a passage configured to allow a sheet to bemanually inserted thereinto; a reading sensor configured to read asurface of the sheet inserted into the passage; and a controllerconfigured to: output a notification after reading a first surface ofthe sheet by the reading sensor, the notification being a notificationto urge a user to read a second surface opposite to the first surface ofthe sheet by the reading sensor; and determine a type of the sheet basedon a reading result of the first surface by the reading sensor and areading result of the second surface by the reading sensor. An imageforming apparatus for forming an image on a sheet based on an imageforming condition according to another aspect of the present disclosureincludes: a passage configured to allow a sheet to be manually insertedthereinto; a reading sensor configured to read a surface of the sheetinserted into the passage; a display; and a controller configured to:control the display to display a screen after reading a first surface ofthe sheet by the reading sensor, the screen being a screen to urge auser to read a second surface opposite to the first surface of thesheet; control the display to display a plurality of candidates of atype of the sheet based on a reading result of the first surface by thereading sensor and a reading result of the second surface by the readingsensor; and control the image forming conditions based on the type ofthe sheet selected from among the plurality of candidates displayed onthe display.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments (with reference to theattached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration view of an image forming apparatus.

FIG. 2A and FIG. 2B are enlarged views of a fixing device.

FIG. 3 is a configuration diagram of a controller.

FIG. 4A and FIG. 4B are explanatory views of a paper type identificationapparatus.

FIG. 5A and FIG. 5B are explanatory views of the paper typeidentification apparatus.

FIG. 6 is an explanatory view of the paper type identificationapparatus.

FIG. 7 is an explanatory view of a line sensor.

FIG. 8 is an illustrative table of a paper type database.

FIG. 9 is a flow chart representing a parameter acquisition process.

FIG. 10 is an exemplary view of an operation screen.

FIG. 11 is an exemplary view of an operation screen.

FIG. 12 is an exemplary view of an operation screen.

FIG. 13 is an exemplary view of an operation screen.

FIG. 14 is a graph explaining relationship between transmittance ofultrasonic waves and basis weight.

FIG. 15 is a flowchart illustrating a paper type identification process.

FIG. 16 is an explanatory diagram illustrating classification of surfaceproperties.

FIG. 17 is an exemplary view of a brand candidate screen.

FIG. 18 is an exemplary view of a brand candidate screen.

DESCRIPTION OF THE EMBODIMENTS

In the following, at least one embodiment of the present disclosure isdescribed with reference to the drawings.

<Image Forming Apparatus>

FIG. 1 is a configuration view of an image forming apparatus accordingto a first embodiment of this embodiment. An image forming apparatus 201according to this embodiment is, for example, a laser beam printer of atandem intermediate-transfer type using an electrophotographic process.The image forming apparatus 201 forms a full-color image or a monochromeimage on a sheet S, which is a recording medium, and outputs the sheet Sbased on image data acquired from an external device, for example, apersonal computer via a network or based on image data acquired from animage reading device 300.

The image forming apparatus 201 has, inside a main body 201A, componentsfor forming an image, and includes, on the top of the main body 201A, animage reading device 300, an operation unit 502, and a paper typeidentification apparatus 100. A delivery space DS for receiving thesheet S to be delivered thereinto after image formation is definedbetween the main body 201A of the image forming apparatus 201 and theimage reading device 300.

The image reading device 300 is a scanner which reads an image from anoriginal to generate image data. The image reading device 300 is used,for example, at the time of processing of copying an original. Theoperation unit 502 is a user interface including an input interface andan output interface. Examples of the input interface include various keybuttons and a touch panel. Examples of the output interface include adisplay and a speaker. A user can input various instructions to theimage forming apparatus 201 via the operation unit 502. The paper typeidentification apparatus 100 is a device for identifying the type of thesheet S that is used by the image forming apparatus 201 for imageformation (printing). Details of the paper type identification apparatus100 will be described later.

The image forming apparatus 201 includes, in the main body 201A, animage forming unit 201B, an intermediate transfer unit 201C, a secondarytransfer unit 201D, a fixing device 201E, and cassette sheet-feedingunits 230.

The cassette sheet-feeding units 230 each feed sheets S from acorresponding one of sheet-feeding cassettes 1 accommodating the sheetsS. The cassette sheet-feeding unit 230 includes a pickup roller 2 and aseparation unit. The separation unit includes a feed roller 3 and aretard roller 4 for separating sheets S sent out from the pickup roller2. The sheets S are fed one by one from the sheet-feeding cassette 1 bythe pickup roller 2 and the separation unit. In this embodiment, aconfiguration in which a plurality of (in this example, four) cassettesheet-feeding units 230 are provided is described. However, any numberof cassette sheet-feeding units 230 may be provided. The sheet S fedfrom the cassette sheet-feeding unit 230 is conveyed to a registrationroller pair 240 along a conveyance path.

The sheet S can be fed from a unit other than the cassette sheet-feedingunit 230, that is, from a manual sheet-feeding unit 235. The manualsheet-feeding unit 235 includes a manual feeding tray 5 for receivingsheets S placed by a user. Similar to the cassette sheet-feeding unit230, the manual sheet-feeding unit 235 includes a pickup roller and aseparation unit, and sheets S are fed one by one from the manual feedingtray 5. The sheet S fed from the manual sheet-feeding unit 235 is alsoconveyed to the registration roller pair 240 along a conveyance path.

The image forming unit 201B is of a four-drum full-color type, andincludes a laser scanner 210 and four process cartridges 211. The fourprocess cartridges 211 form toner images of four colors, specifically,yellow (Y), magenta (M), cyan (C), and black (K). Each process cartridge211 includes a photosensitive drum 212, a charging device 213, and adeveloping device 214. Toner cartridges 215 are arranged above theprocess cartridges 211. The toner cartridges 215 replenish therespective developing devices 214 with toner.

The intermediate transfer unit 201C includes an intermediate transferbelt 216 wound around a drive roller 216 a and a tension roller 216 b.On an inner side of the intermediate transfer belt 216, there areprovided four primary transfer rollers 219 which are in abutment againstthe intermediate transfer belt 216 at positions opposing thephotosensitive drums 212. The intermediate transfer belt 216 is rotatedin the arrow direction by the drive roller 216 a driven by a drive unit(not shown).

The secondary transfer unit 201D includes a secondary transfer roller217 provided so as to sandwich the intermediate transfer belt 216 at aposition opposing the drive roller 216 a. The fixing device 201E isprovided on a downstream side of the secondary transfer roller 217 in aconveyance direction of the sheet S, and includes a pressure roller 220a and a heating roller 220 b. On a downstream side of the fixing device201E in the conveyance direction of the sheet S, there are arranged afirst delivery roller pair 225 a, a second delivery roller pair 225 b,and a duplex-printing reversing unit 201F. The duplex-printing reversingunit 201F includes a reversing roller pair 222 and a re-conveyancepassage R. The reversing roller pair 222 is rotatable in forward andreverse directions. The re-conveyance passage R allows the sheet Shaving an image formed on one side thereof to be conveyed to the imageforming unit 201B.

The image forming apparatus 201 having the configuration as describedabove operates as follows. The image forming apparatus 201 acquiresimage data from the image reading device 300 or from an external deviceand forms an image corresponding to the image data on the sheet S. Atthis time, the image forming apparatus 201 performs each process of theimage formation based on operation conditions given in accordance with atype of the sheet S.

The image forming unit 201B uses the charging device 213 to uniformlycharge surfaces of the photosensitive drums 212 to an electric potentialhaving a predetermined polarity. The laser scanner 210 irradiates theuniformly charged surfaces of the photosensitive drums 212 withcorresponding laser beams modulated based on the image data. In thisway, electrostatic latent images for corresponding colors (yellow,magenta, cyan, and black) are formed on the respective surfaces of thephotosensitive drums 212.

The image forming unit 201B uses the developing devices 214 to developthe electrostatic latent images formed on the photosensitive drums 212.The electrostatic latent images are developed on the photosensitivedrums 212 with toners of corresponding colors so that toner images ofthe corresponding colors are formed on the photosensitive drums 212. Thetoner images are sequentially transferred from the photosensitive drums212 to the rotating intermediate transfer belt 216 in superimposition bythe primary transfer rollers 219. In this way, a full-color toner imageis formed on the intermediate transfer belt 216. The intermediatetransfer belt 216 rotates to convey the toner image to the secondarytransfer unit 201D.

Concurrently with such operation of forming a toner image, the sheets Sare conveyed one by one by the cassette sheet-feeding unit 230 or themanual sheet-feeding unit 235 to the registration roller pair 240. Theregistration roller pair 240 corrects the skew of the sheet S conveyedto the registration roller pair 240. After the skew is corrected, thesheet S is conveyed by the registration roller pair 240 to the secondarytransfer unit 201D in synchronization with the timing at which the tonerimage borne on the intermediate transfer belt 216 is conveyed to thesecondary transfer unit 201D. The secondary transfer unit 201D transfersthe full-color toner image from the intermediate transfer belt 216 ontothe sheet S with secondary transfer bias applied to the secondarytransfer roller 217.

The sheet S having the toner image transferred thereto is conveyed tothe fixing device 201E. The fixing device 201E sandwiches and conveysthe sheet S with a roller nip portion defined by the pressure roller 220a and the heating roller 220 b. The fixing device 201E heats the sheet Swith the heating roller 220 b at the time of sandwiching and conveyingthe sheet S, to thereby melt and mix the toners of respective colors onthe sheet S. Further, the fixing device 201E presses the sheet S withthe pressure roller 220 a, to thereby fix the melted and mixed toners tothe sheet S. At this time, the viscosity of the melted toner generates asticking force to the heating roller 220 b on the sheet S.

FIG. 2A and FIG. 2B are enlarged views of the fixing device 201E. Whenthe stiffness (strength) of the sheet S is small, the sticking force tothe heating roller 220 b generated on the sheet S may cause the sheet Sto be rolled up by the heating roller 220 b being rotated (FIG. 2B).Thus, a separation plate 202 which separates the sheet S is provided ona downstream side of the heating roller 220 b in the conveyancedirection of the sheet S (FIG. 2A).

The image forming apparatus 201 may determine a state of the separationplate 202 in accordance with a type of the sheet S. For example, whenthe sheet S of a type having a small stiffness is subjected to imageformation, the separation plate 202 is arranged such that a distal endof the separation plate 202 is in contact with a surface of the heatingroller 220 b as illustrated in FIG. 2A, to thereby separate the sheet Sfrom the heating roller 220 b. When the sheet S of a type having a largestiffness is subjected to image formation, the sheet S is not rolled upby the heating roller 220 b. Thus, the separation plate 202 is arrangedsuch that the distal end of the separation plate 202 is not in contactwith the surface of the heating roller 220 b. In this way, the surfaceof the heating roller 220 b can be prevented from being worn by theseparation plate 202.

The sheet S having the image fixed thereto is delivered to the deliveryspace DS by any one of the first delivery roller pair 225 a or thesecond delivery roller pair 225 b. The sheet S is placed on a placementportion 223 provided in a protruding manner on a bottom surface of thedelivery space DS. When images are formed on both sides of the sheet S,the sheet S having an image fixed on one side thereof is conveyed by areversing roller pair 222 to the re-conveyance passage R. The sheet S isconveyed again to the image forming unit 201B, and an image is formed onanother side of the reversed sheet S.

<Controller>

FIG. 3 is an explanatory diagram of a controller which controls theoperation of such image forming apparatus 201. A controller 400 is, forexample, an information processing device including a central processingunit (CPU). The controller 400 may be achieved by, for example, amicroprocessor unit (MPU) or an application specific integrated circuit(ASIC). The controller 400 controls the above-mentioned image formingprocessing performed by the image forming apparatus 201. Further, inthis embodiment, the controller 400 is connected to the paper typeidentification apparatus 100 to control the paper type identificationapparatus 100. A memory 401 and the operation unit 502 are connected tothe controller 400. The memory 401 includes a paper type database 402.The paper type database 402 stores pieces of information such as afeature amount of various brands of sheets, parameters of operationcondition of each component at the time of optimum image formation,whether or not to allow passage of sheets in the image forming apparatus201, and usable sheet feeding ports.

The paper type identification apparatus 100 includes an informationprocessing unit 160. The information processing unit 160 is aninformation processing device achieved by, for example, a CPU, an MPU,or an ASIC. The information processing unit 160 is communicablyconnected to the controller 400 and can operate in cooperation with thecontroller 400. The information processing unit 160 has an upstreamsheet sensor 104, a downstream sheet sensor 105, a mechanical physicalproperty measurement unit 102, and a surface property measurement unit103 connected thereto. The mechanical physical property measurement unit102 includes an ultrasonic wave sensor 120 and a sheet thickness sensor140. The surface property measurement unit 103 includes an opticalsensor 150. The information processing unit 160 controls operations ofthe upstream sheet sensor 104, the downstream sheet sensor 105, themechanical physical property measurement unit 102, and the surfaceproperty measurement unit 103 and acquires respective measurementresults.

The upstream sheet sensor 104 is a sensor to detect insertion of thesheet S to the paper type identification apparatus 100. The informationprocessing unit 160 starts a measurement sequence of the feature amountof the Sheet S upon detection of the sheet S by the upstream sheetsensor 104. The downstream sheet sensor 105 is a sensor to detect thatthe sheet S reached an inner-most part (an abutment portion, describedlater) to which the sheet S in the paper type identification apparatus100 can be inserted. The ultrasonic wave sensor 120 is a sensor used formeasurement of the basis weight of the Sheet S. The sheet thicknesssensor 140 is a sensor used for the measurement of the sheet thicknessof Sheet S. The optical sensor 150 is a sensor used for measurement ofsurface property information such as an integrated value of thedifference between adjacent pixels of the Sheet S, brightness, and thelike. The integrated value of the difference between adjacent pixels isan integrated value of the difference between detection values(measurement results) of adjacent pixels. The optical sensor 150 outputsthe brightness value for each pixel as a measurement result. Theinformation processing unit 160 stores the measurement result, andgenerates surface property information based on the measurement result.The details of the ultrasonic wave sensor 120, the sheet thicknesssensor 140, and the optical sensor 150 are described later.

The information processing unit 160 transmits, to the controller 400,the mechanical physical property information (basis weight and sheetthickness) acquired by the mechanical physical property measurement unit102 and the surface property information acquired by the surfaceproperty measurement unit 103. The controller 400 determines the papertype of the sheet S based on the acquired surface property. Then, thecontroller 400 identifies, by the paper type database 402, the brand ofthe sheet S based on the paper type and the mechanical physical propertyinformation (basis weight and sheet thickness) and display the brand ona display of the operation unit 502.

<Type of Sheet Used for Image Forming Apparatus>

Operation conditions of each component for each process given at thetime of image forming processing (conveyance speed and fixingtemperature given at the time of fixing, and transfer voltage given atthe time of secondary transfer) differ depending on the feature amount(physical property), such as a basis weight, a stiffness, a surfaceproperty, and a material, of the sheet S subjected to image formation.Thus, it is important to grasp in advance a type of the sheet S to beused at the time of image formation.

There may be some limitations in setting the sheet S to a sheet feedingport of the image forming apparatus 201. The sheet feeding port is thesheet-feeding cassette 1 or the manual feeding tray 5. For example, somethick paper sheets having a high stiffness can be fed only from themanual feeding tray 5 with a conveyance path having a small curvature.Coated paper sheets having a smooth surface texture and a strongadhesion between sheets are required to be fed one by one from themanual feeding tray 5. Paper sheets made of pulp as a raw materialgenerally have different bending stiffnesses in length and widthdirections because of bias in orientation directions of pulp fibers(fiber orientation) that occurs due to a manufacturing method. Thus, forsome paper sheets made of pulp as a raw material, there is given arecommended orientation of the sheet in length and width directions atthe time of setting the sheet to the sheet feeding port so that thebending stiffness against the bending in the conveyance path becomessmaller. Further, for one-side coated paper sheets obtained by coatingonly one side of a plain paper sheet, an orientation in up-and-downdirections is designated at the time of setting in order to performimage formation on the coated side.

There are also some sheets which cannot be used in the image formingapparatus 201. For example, in a case of a thick paper sheet having anexcessively high stiffness, conveyance of the sheet may be stopped dueto resistance generated at the time of conveying the sheet along a bentconveyance path. A thin paper sheet having an excessively low stiffnessis strongly affected by the sticking force generated between the meltedtoner and the heating roller 220 b at the time of passage through thefixing device 201E as described above. Thus, there is a possibility thata paper sheet having an excessively low stiffness is not separated fromthe heating roller 220 b by the separation plate 202 and is directlywound around the heating roller 220 b (FIG. 2B). Further, in a case of asynthetic paper sheet which is not made of pulp but of a synthetic resinas raw material, there is a possibility that the sheet is melted byheating in the fixing device 201E and thereby contaminate the heatingroller 220 b.

<Paper Type Identification Apparatus>

FIG. 4A, FIG. 4B, FIG. 5A, FIG. 5B, and FIG. 6 are explanatory views ofthe paper type identification apparatus 100. FIG. 4A and FIG. 4B show astate before the sheet S is inserted into the paper type identificationapparatus 100. FIG. 5A and FIG. 5B show a state in which the sheet S hasbeen inserted into the paper type identification apparatus 100. FIG. 4Aand FIG. 5A are views of the paper type identification apparatus 100 asseen from a lateral side (front side of the image forming apparatus 201of FIG. 1 ). FIG. 4B and FIG. 5B are views of the paper typeidentification apparatus 100 as seen from an upper side. FIG. 6 is aview of the paper type identification apparatus 100 as seen in aninsertion direction of the sheet S.

The paper type identification apparatus 100 has a groove portion 101serving as a passage configured to allow the sheet S subjected toidentification to be inserted thereinto, and measures the feature amountof the sheet S inserted from the groove portion 101. The insertion ofthe sheet S is performed manually by a user. The groove portion 101includes an upper block 109 in an upper part and a lower block 110 in alower part. The groove portion 101 is a passage configured to allow asheet to be manually inserted.

On a groove-portion inner side of the lower block 110, a sheet pressingmember 106 is provided. The sheet pressing member 106 is urged by anurging member 107 toward the upper block 109 side. The sheet S isinserted while pushing away the sheet pressing member 106 downward. Theupper block 109 projects at an end portion of the sheet pressing member106 (innermost portion to which the sheet S can be inserted) toward thelower block 110 side, thereby forming an abutment portion 108. Theabutment portion 108 restricts the insertion of the sheet S. Thus, thesheet S can only be inserted to the abutment portion 108. Theinformation processing unit 160 is arranged on an inner side beyond theabutment portion 108.

The measurement unit for the feature amount of the sheet S includes themechanical physical property measurement unit 102 and the surfaceproperty measurement unit 103, as described above. As the sheet S passesthrough the measurement unit, the feature amount of the sheet S, such asbasis weight, a surface property, and a sheet thickness, are acquired.The upstream sheet sensor 104 is arranged on an upstream side of thesurface property measurement unit 103 in the insertion direction of thesheet S. The downstream sheet sensor 105 is arranged in the vicinity ofthe abutment portion 108 on the upstream side in the insertion directionof the sheet S. That is, the upstream sheet sensor 104 is arranged at aninsertion start position of the sheet S, and the downstream sheet sensor105 is arranged at an insertion end position of the sheet S. Theupstream sheet sensor 104 and the downstream sheet sensor 105 eachdetect the inserted sheet S.

In the mechanical physical property measurement unit 102, as illustratedin FIG. 6 , there are provided an ultrasonic wave emitter 130 on thelower block 110 side and an ultrasonic wave receiver 131 on the upperblock 10) side such that the ultrasonic wave emitter 130 and theultrasonic wave receiver 131 are arranged across an insertion passagealong which the sheet S is to be inserted. The ultrasonic wave emitter130 and the ultrasonic wave receiver 131 form the ultrasonic wave sensor120. The mechanical physical property measurement unit 102 transmits andreceives ultrasonic waves with the ultrasonic wave sensor 120 via theinsertion passage of the sheet S, thereby being capable of detecting abasis weight of the sheet S. The basis weight is a mass of the sheet Sper unit area, and is represented by a unit “gsm”.

The ultrasonic wave emitter 130 and the ultrasonic wave receiver 131 areeach formed of a piezoelectric element (also referred to as “piezoelement”), which is an element for mutual conversion between amechanical displacement and an electric signal, and an electrodeterminal. The ultrasonic wave emitter 130 generates ultrasonic wavesthrough oscillation of the piezoelectric element in response to input ofa pulse voltage having a predetermined frequency to the electrodeterminal. The generated ultrasonic waves propagate through air. Uponarrival of the ultrasonic waves to the sheet S, the ultrasonic wavescause the sheet S to vibrate. The ultrasonic waves generated in theultrasonic wave emitter 130 propagate to the ultrasonic wave receiver131 via the sheet S. The piezoelectric element of the ultrasonic wavereceiver 131 causes the electrode terminal to generate an output voltagecorresponding to an amplitude of the received ultrasonic waves. Theoutput voltage has a voltage value corresponding to the basis weight ofthe sheet S. The output voltage is transmitted as a measurement value tothe information processing unit 160.

As compared to a case in which the sheet S is absent between theultrasonic wave emitter 130 and the ultrasonic wave receiver 131, theoutput voltage generated by the ultrasonic waves transmitted via thesheet S is reduced. The information processing unit 160 calculates atransmittance of the sheet S in accordance with a ratio of an outputvoltage given in the presence of the sheet S and an output voltage givenin the absence of the sheet S. The transmittance of the ultrasonic wavesvaries depending on the thickness of the sheet S. Thus, the informationprocessing unit 160 can estimate the basis weight of the sheet S with aconversion formula for an ultrasonic wave transmittance coefficient anda basis weight. In this way, the basis weight of the sheet S is detectedwith the ultrasonic wave sensor 120.

The upstream sheet sensor 104 which is provided in the upper block 109and located on the upstream side of the surface property measurementunit 103 in the insertion direction of the sheet S detects insertion ofthe sheet S into the paper type identification apparatus 100. Thedownstream sheet sensor 105 which is provided in the upper block 109 andlocated on the downstream side of the surface property measurement unit103 in the insertion direction of the sheet S detects that thecompletely inserted sheet S has reached the abutment portion 108.

The sheet thickness sensor 140 is arranged near the abutment portion108. The sheet thickness sensor 140 is of a lever type. In the sheetthickness sensor 140, a lever tilts in accordance with a thickness ofthe sheet S so that an encoder rotates in accordance with the tiltingamount of the lever. During rotation of the encoder, the sheet thicknesssensor 140 transmits a pulse signal as a measurement value of the sheetthickness to the information processing unit 160. The sheet thicknesssensor 140 is arranged somewhat on the downstream side in the insertiondirection of the sheet S with respect to the downstream sheet sensor 105so that the sheet thickness can be measured upon detection of the sheetS by the downstream sheet sensor 105.

As described above, the surface property measurement unit 103 includesthe optical sensor 150 for detecting the surface property of the sheetS. The optical sensor 150 includes a light emitter 132 and a line sensor133. The optical sensor 150 is a contact image sensor (CIS), forexample. The light emitter 132 is, for example, a light emitted diode(LED). The line sensor 133 is formed of an array of a plurality of lightreceiving elements. For example, the line sensor 133 may be a CMOS linesensor including CMOS sensors as light receiving elements.

As illustrated in FIG. 6 , the surface property measurement unit 103(optical sensor 150) includes the light emitter 132 and the line sensor133 on the upper block 109 side. In the line sensor 133, a plurality oflight receiving elements are arranged in a direction orthogonal to theinsertion direction of the sheet S in the paper type identificationapparatus 100. Thus, the line sensor 133 detects the surface of thesheet S along one line in the direction crossing the insertion directionof the sheet S. The line sensor 133 can detect a sheet surface regionwith a resolution corresponding to a pixel size and an imagingmagnification of the optical system.

A light amount of reflected light from the sheet S to the line sensor133 changes according to the surface property of the sheet S. Forexample, as compared to a plain paper sheet, a surface of a coated papersheet has a higher degree of smoothness (i.e., there is littleunevenness). Therefore, as compared to the plain paper sheet, the coatedpaper sheet has larger amount of specular light and smaller amount ofdiffused reflection light (diffusion light). That is, the amount of thereflected light substantially represents the degree of smoothness of thesurface of the sheet S. By using at least one of a specular reflectionlight amount and a diffused reflection light amount which enters theline sensor 133, the type of the sheet S can be determined. The linesensor 133 is configured such that the reflected light may be sampledbased on a clock signal of a predetermined sampling frequency. Themethod of measuring surface property of the sheet S using the surfaceproperty measurement unit 103 in the present embodiment is performedusing two or more times of sampling results.

The surface property measurement unit 103 is required to hold the sheetS at an optical focus position. Thus, the urging member 107 urges thesheet S toward the surface property measurement unit 103 side by thesheet pressing member 106 to stabilize a posture of the sheet S. In thisway, variation in position and posture of the sheet S at the time ofdetecting the surface of the sheet S is reduced, therefore, the surfaceproperty measurement unit 103 can stably detect the surface property.The urging member 107 is set so as to press the inserted sheet S towardthe surface property measurement unit 103 side with a force of about 100gf.

FIG. 7 is an explanatory view of the line sensor 133. The line sensor133 can detect an image of n pixels in a direction orthogonal to theinsertion direction of the sheet S at once. Therefore, n light receivingelements are arranged in series in the direction orthogonal to theinsertion direction of the sheet S, for example.

<Surface Property Information>

The information processing unit 160 performs a digital process on theimage detected by the optical sensor 150 to acquire a detection value(luminance value) for each pixel. The detection value (luminance value)is accumulated in the memory inside the information processing unit 160.The information processing unit 160 acquires the integrated value ofdifference between adjacent pixels and brightness as surface propertyinformation based on the detection value accumulated in the memory. Theinformation processing unit 160 accumulates the surface propertyinformation in the memory.

The integrated value of difference between adjacent pixels is, asdescribed above, the integrated value of the difference between thedetection values (luminance value) of adjacent pixels in a direction ofone line, and serves as an index representing unevenness of the surfaceof the sheet S. In FIG. 7 , assuming that the detection value (samplingresult of one time) of each pixel is “A1” to “An” according to theposition of a pixel, the integrated value of difference between adjacentpixels k is represented by the following formulas:

k=(A2−A1)+(A3−A2) . . . +(An−A(n−1)).

The brightness is an integrated value of the detection values of thepixels detected by the optical sensor 150, and is a parameter correlatedwith the reflectance (lightness) of the sheet S. For example, atransparent film made of a resin such as PET has a small amount of thereflected light, and hence the brightness is measured as being low. Asto the sheet S that has a geometrical irregularity shape on its surfaceas in a case of an embossed paper sheet, it has a large luminancedifference between adjacent pixels due to the irregularities, and hencethe integrated value of difference between adjacent pixels is large. Arecycled paper sheet has a non-uniform fiber orientation, and pulpfibers are shortened due to several recycling processes. As a result,the measured surface property tends to be rough. The coated paper sheetappears to have less irregularities due to the presence of the coatinglayer on the surface. Thus, the integrated value of difference betweenadjacent pixels tends to be small.

<Paper Type Database>

FIG. 8 is an illustrative table of the paper type database 402 stored inthe memory 401 of the image forming apparatus 201. In the paper typedatabase 402, the feature amount measured by the paper typeidentification apparatus 100 is stored in relation with brandinformation. The feature amount includes physical property value (basisweight, sheet thickness), surface property information (first surfaceproperty) that represents surface property of a front surface (printsurface), and surface property information (second surface property)that represents surface property of a back surface. The surface propertyinformation further includes the integrated value of difference betweenadjacent pixels and brightness.

<Paper Type Identification>

FIG. 9 is a flowchart for representing parameter acquisition processingfor identifying the sheet type of the sheet S. FIG. 10 , FIG. 11 , FIG.12 , and FIG. 13 are exemplary views of operation screens displayed on adisplay of the operation unit 502 during the parameter acquisitionprocessing. Upon using the sheet S, the user displays the operationscreen shown in FIG. 10 on the display of the operation unit 502. Thisoperation screen includes a “sheet manual selection” button and a “sheetautomatic identification” button. The “sheet manual selection” buttonallows a user to manually input a type of the sheet S. The “sheetautomatic identification” button allows the paper type identificationapparatus 100 to automatically select a type of the sheet S. In thisembodiment, in response to selection of the “sheet automaticidentification” button by a user from the selection screen with use ofthe operation unit 502, the selected content is input to the controller400.

In a case where the controller 400 acquires the information indicatingthat the “sheet automatic identification” button has been selected fromthe operation unit 502, the controller 400 sets an operation mode to anautomatic identification mode for the sheet S (Step S1). Upon settingthe automatic identification mode, the controller 400 instructs theinformation processing unit 160 of the paper type identificationapparatus 100 to measure the sheet S. According to this instruction, theinformation processing unit 160 performs initialization processing forthe mechanical physical property measurement unit 102 and the surfaceproperty measurement unit 103. Further, the controller 400 displays, ina case where the automatic identification mode is set, the operationscreen shown in FIG. 11 on the display of the operation unit 502. Thisoperation screen contains a “one-side reading” button for measuring onlyone side of the sheet S. and a “double-sided reading” button formeasuring both sides of the sheet S. The user selects, by selecting oneof the buttons, one of one-side measurement of the sheet S or thedouble-sided measurement of the sheet S. The controller 400 acquiresinformation representing that “one-side reading” button has beenselected or “double-sided reading” button has been selected from theoperation unit 502 (Step S2). After selecting the surface to bemeasured, the controller 400 displays the operation screen shown in FIG.12 on the display of the operation unit 502 to thereby instruct the userto insert the sheet S (Step S3). The user starts insertion of the sheetS in the groove portion 101 of the paper type identification apparatus100, according to this operation screen.

After completion of an initialization process in the process of Step S1,the information processing unit 160 waits for the insertion of the sheetS in the groove portion 101. Due to the insertion of the sheet S in thegroove portion 101 by the user according to the operation screen of FIG.12 , the information processing unit 160 starts measurement of thefeature amount of the front surface (first surface) of the sheet S (StepS4). The measurement of the feature amount is performed as follows. Itis note that, after completion of the measurement of the feature amountof the front surface (first surface), the information processing unit160 notifies the controller 400 of completion of the measurement.

Triggered by the detection of the sheet S by the upstream sheet sensor104, the information processing unit 160 controls the surface propertymeasurement unit 103 (optical sensor 150) to start measurement of one ormore surface properties of the sheet S after a predetermined time t1 haselapsed. The information processing unit 160 controls the optical sensor150 to read the sheet S, and sequentially acquires the reading results(detection values). The optical sensor 150 measures the surface propertyof the sheet S by scanning the conveyed sheet S two or more times atintervals of predetermined time. The information processing unit 160performs the above described processes to the reading result (detectionvalue) by the optical sensor 150, and generates the surface propertyinformation to accumulates the same in an internal memory.

The information processing unit 160 controls the mechanical physicalproperty measurement unit 102 to start measurement of one or morephysical properties of the sheet S after a predetermined time t2 haselapsed from the detection of the sheet S by the upstream sheet sensor104. The information processing unit 160 measures a transmittance of thesheet S for ultrasonic waves with use of the ultrasonic wave sensor 120,converts the measurement values into pieces of basis weight information,and accumulates the pieces of basis weight information in the memory.FIG. 14 is an explanatory graph of a relationship between thetransmittance of ultrasonic waves and the basis weight. The informationprocessing unit 160 holds a conversion formula or a conversion tableindicating such relationship between the transmittance of ultrasonicwaves and the basis weight. The information processing unit 160 performsthe conversion of the measured value into the basis weight with use ofsuch conversion formula or conversion table. As a result, measurement ofphysical properties, the basis weight information of the sheet S isstored in the memory of the information processing unit 160. Further,triggered by the detection of the sheet S by the upstream sheet sensor104, the information processing unit 160 waits counts from pulse signalsoutput from the sheet thickness sensor 140.

The information processing unit 160 waits until the downstream sheetsensor 105 detects the sheet S. The downstream sheet sensor 105 detectsthe sheet S when the sheet S is inserted up to the innermost abutmentportion 108. In a case where the downstream sheet sensor 105 detects thesheet S, the information processing unit 160 acquires the pulse signal,which is the measurement value, from the sheet thickness sensor 140. Theinformation processing unit 160 measures the sheet thickness of thesheet S based on the number of acquired pulse signals (pulse count). Thesheet thickness of the sheet S is accumulated in the memory of theinformation processing unit 160. In a case where the downstream sheetsensor 105 detects the sheet S, the information processing unit 160stops reading of the sheet S by the optical sensor 150 of the surfaceproperty measurement unit 103.

After receiving the completion of the measurement of the feature amountof the surface from the information processing unit 160, the controller400 checks whether the one-side measurement or the double-sidedmeasurement has been selected in the process of Step S2 (Step S5). In acase where the one-side measurement has been selected (Step S5: Y), thecontroller 40 acquires the surface measurement result (feature amount)of the front surface (first surface) from the information processingunit 160 to perform the paper type identification process, which isdescribed later, and displays brand candidates for the sheet on thedisplay of the operation unit 502 (Step S6). The user checks the brandcandidates displayed on the display to determine whether to measure theback surface (second surface) or not. The user instructs whether tomeasure the back surface by the operation unit 502 according to thedetermination result. For example, the user determines to measure theback surface in a case where the user's own expected brand is notincluded in the brand candidates.

The controller 400 acquires instructions of whether to measure the backsurface or not from the operation unit 502 (Step S7). In a case where itis determined to not measure the back surface (Step S7: N), thecontroller 400 ends the parameter acquisition processing. In a casewhere it is determined to measure the back surface (Step ST Y), thecontroller 400 displays the operation screen shown in FIG. 13 on thedisplay of the operation unit 502 to thereby instruct the user to insertthe sheet S (Step S8). Further, in a case where the double-sidedmeasurement has been selected, (Step S5: N), the controller 400 does notperform the processes of Steps S6 and S7, rather it displays theoperation screen shown in FIG. 13 on the display of the operation unit502 to thereby instruct the user to insert the sheet S (Step S8). Withthe operation screen of FIG. 13 , a notification is given to the user,and the notification is to urge the user to insert the sheet S into thepaper type identification apparatus 100 with the front surface and theback surface of the sheet S reversed.

The information processing unit 160 measures the feature amount of theback surface (second surface) of the inserted sheet S by the sameprocess as the process of Step S4 (Step S9). It is note that, aftercompletion of the measurement of the feature amount of the back surface(second surface), the information processing unit 160 notifies thecontroller 400 of the completion of the measurement. After receiving thecompletion of the measurement of the feature amount of the back surfacefrom the information processing unit 160, the controller 400 acquiresthe measurement result (feature amount) of both the front surface andthe back surface from the information processing unit 160 to perform thepaper type identification process, which is described later, anddisplays brand candidates for the sheet on the display of the operationunit 502 (Step S10). The parameter acquisition process is completed asdescribed above.

FIG. 15 is a flowchart for representing the sheet type identificationprocessing performed in the process of S6 and the process of Step S10.Here, the paper type identification process is described for each ofone-side measurement (process of Step S6) and double-sided measurement(process of Step S10).

In a case of one-side measurement, the controller 400 identifies thepaper type based on the measurement result (feature amount) of the frontsurface (first surface). The controller 400 performs classification ofthe type of the sheet S based on the measurement results of the surfaceproperty of the sheet S (Step S21). FIG. 16 is an explanatory diagram ofthe classification of the surface properties. In FIG. 16 , surfaceproperties of the sheets S are measured and classified in advance, asindices of surface properties, with use of a matrix including thevertical axis representing the integrated value of difference betweenadjacent pixels and the horizontal axis representing the brightness. Thecontroller 400 classifies the type of the sheet S by referring to thematrix based on the surface property information (integrated value ofdifference between adjacent pixels and brightness) that are obtainedfrom the detection value detected by the optical sensor 150. Thecontroller 400 classifies the type of the sheet S by selecting, in thebrands in the paper type database 402, a brand having the first surfaceproperty that matches the measurement result (surface propertyinformation).

The controller 400 selects, in the classification by the surfaceproperty, brands having basis weight within a predetermined range (forexample, +5 gsm) from the measured basis weight (Step S22). Further, thecontroller 400 selects, in the selected brands, brands having sheetthickness within a predetermined range (for example, +5 μm) from themeasured sheet thickness (Step S23). The controller 400 displays thebrand candidates for the selected sheet on the display of the operationunit 502 (Step S24). By using the basis weight and the sheet thicknessfor the parameter of paper type selection as well as the surfaceproperty information, further selection of the brand is performed andbrand identification accuracy is improved.

FIG. 17 is an explanatory view of the brand candidate screen displayedin this way. The brand candidate screen of FIG. 17 is displayed in theprocess of Step S6 in FIG. 9 . In the brand candidate screen shown inFIG. 17 , a “sheet automatic identification back surface measurement”button is provided so that measurement of the back surface can beinstructed in the process of Step S7. By selecting this button, it isdetermined that the measurement of the back surface will be performed inthe process of Step S7. The character of “recommended” is labeled on thepaper type that best matches in the measurement result by the mechanicalphysical property measurement unit 102 and the surface propertymeasurement unit 103.

In the double-sided measurement, the controller 400 identifies the papertype, as in the single-sided measurement, based on the surface propertyinformation (integrated value of difference between adjacent pixels andbrightness) of each of the front surface and the back surface. Since themeasured value of the basis weight is detected from the transmissivityof the ultrasonic wave, as to the front surface and the back surface,there is no difference in the measured value. Also, in the sheetthickness, as to the front surface and the back surface, there is nodifference in the measured value. Therefore, as to the basis weight andthe sheet thickness, the average value of measured value of the frontsurface and that of the back surface is used.

The controller 400 identifies the paper type based on the measurementresult (feature amount) of the front surface (first surface) and that ofthe back surface. The controller 400 performs classification of the typeof the sheet S based on the measurement results of the front surfaceproperty and the back surface property of the sheet S (Step S21). Thecontroller 400 selects, in the brands in the paper type database 402, abrand having the first surface property that matches the measurementresult of the front surface (surface property information) and havingthe second surface property that matches the measurement result of theback surface (surface property information). Hereinafter, the brandselected at this time is referred to as “first brand.” It is noted that,in the measurement of the sheet S, the user might insert the sheet Swith the front surface and the back surface reversed. Therefore, thecontroller 40 selects, in the brands in the paper type database 402, abrand (second brand) having the first surface property that matches themeasurement result of the back surface (surface property information)and having the second surface property that matches the measurementresult of the front surface (surface property information). Thus, theclassification of the type of sheet S is performed.

The controller 400 selects, in the classification by the surfaceproperty (first brand and second brand), brands having basis weightwithin a predetermined range (for example, ±5 gsm) from the measuredbasis weight (Step S22). Further, the controller 400 selects, in theselected brands, brands having sheet thickness within a predeterminedrange (for example, ±5 μm) from the measured sheet thickness (Step S23).The controller 400 displays the brand candidates for the selected sheeton the display of the operation unit 502 (Step S24). By using the basisweight and the sheet thickness for the parameter of paper type selectionas well as the surface property information, brand identificationaccuracy is improved.

FIG. 18 is an explanatory view of the brand candidate screen displayedin this way. The brand candidate screen of FIG. 18 is displayed in theprocess of Step S10 in FIG. 10 . To accommodate when the paper typewhich the user wishes to select is not included in the brand candidates,a “sheet automatic identification remeasurement” button is provided inthe brand candidate screen of FIG. 18 . By selecting this button, theprocess shown in FIG. 9 is performed again. The character of“recommended” is labeled on the paper type that best matches in themeasurement result by the mechanical physical property measurement unit102 and the surface property measurement unit 103.

As described above, the paper type identification apparatus 100 of thepresent embodiment notifies a user, after the measurement of one surfaceof the sheet has been completed, to reverse sheet S and insert the same.By measuring the back surface, incorrect detection of the brandclassification due to the influence of the difference of the featureamount of front surface and the back surface can be prevented. Thus,even in a case where a measurement device that can perform onlyone-sided measurement is used, the paper type identification apparatus100 of the present embodiment can accurately identify the paper type ofthe sheet.

The information processing unit 160 is provided inside the paper typeidentification apparatus 100, and the information processing unit 160processes the measurement results given by the mechanical physicalproperty measurement unit 102 and the surface property measurement unit103 and sends the processed results to the controller 400 of the imageforming apparatus 201. However, the processing of those measurementresults may be performed directly by the controller 400. In this case,the functions of the information processing unit 160 are included in thecontroller 400. Further, the paper type identification apparatus 100sends the measurement results given by the mechanical physical propertymeasurement unit 102 and the surface property measurement unit 103directly to the controller 400.

In this embodiment, the image forming apparatus 201 includes the papertype database 402. However, the paper type identification apparatus 100may include the paper type database 402. In this case, specification ofa brand of the sheet S performed by the controller 400 is performed bythe information processing unit 160 of the paper type identificationapparatus 100. Further, description has been made of the example inwhich the sheet detection by the upstream sheet sensor 104 is used as atrigger for starting the process. However, it is also possible to usethe sheet detection by the downstream sheet sensor 105 as a trigger forstarting the process. In this case, the surface property measurement isperformed at the time of drawing out the sheet S from the paper typeidentification apparatus 100. The encoder rotation of the sheetthickness sensor 140 may be detected in place of the encoder rotation ofthe downstream sheet sensor 105, and the zone of reading by the surfaceproperty measurement unit 103 may be determined based on the timing ofthe detection.

In the above, description has been made of the example in which theoperation conditions (control parameters) of the image forming apparatus201 are determined through selection of a sheet classification and asheet brand in accordance with characteristics detected by the papertype identification apparatus 100. The paper type identificationapparatus 100 may be a sheet physical property measurement device, andmay determine control parameters directly from measured feature amounts(physical property values) of a sheet. Further, the paper type database402 and the controller 400 may be provided on a cloud. In such a case,as long as the image forming apparatus 201 is connected to the cloud viaa network, the latest sheet type setting information and identificationalgorithm can always be selected.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2022-056636, filed Mar. 30, 2022, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A paper type identification apparatus comprising:a passage configured to allow a sheet to be manually inserted thereinto;a reading sensor configured to read a surface of the sheet inserted intothe passage; and a controller configured to: output a notification afterreading a first surface of the sheet by the reading sensor, thenotification being a notification to urge a user to read a secondsurface opposite to the first surface of the sheet by the readingsensor; and determine a type of the sheet based on a reading result ofthe first surface by the reading sensor and a reading result of thesecond surface by the reading sensor.
 2. The paper type identificationapparatus according to claim 1, further comprising a display to displaythe type of the sheet.
 3. The paper type identification apparatusaccording to claim 1, wherein the controller is configured to: perform afirst mode and a second mode, the first mode being a mode in which thetype of the sheet is determined based on both the reading result of thefirst surface by the reading sensor and the reading result of the secondsurface by the reading sensor, and the second mode being a mode in whichthe type of the sheet is determined based on the reading result of thefirst surface by the reading sensor; and output, in the first mode,after reading the first surface of the sheet by the reading sensor, thenotification to urge the user to read the second surface of the sheet bythe reading sensor.
 4. The paper type identification apparatus accordingto claim 3, wherein the controller is configured to: not urge, in thesecond mode, after reading the first surface of the sheet by the readingsensor, the user to read the second surface of the sheet by the readingsensor and; determine the type of the sheet based on the reading resultof the first surface by the reading sensor.
 5. The paper typeidentification apparatus according to claim 3, wherein the controller isconfigured to: receive user instruction information to instruct toperform the first mode; and select the first mode based on the userinstruction information.
 6. The paper type identification apparatusaccording to claim 3, further comprising a display to display a screento allow the user to select whether to perform the first mode, whereinthe display is configured to display the screen after reading the firstsurface of the sheet by the reading sensor.
 7. The paper typeidentification apparatus according to claim 1, further comprising asheet sensor configured to detect the sheet that has arrived at adetection position on downstream of the reading sensor in an insertiondirection in which the sheet is inserted, wherein the controller isconfigured to acquire the reading result of the first surface that isread by the reading sensor after detecting the sheet by the sheetsensor.
 8. An image forming apparatus for forming an image on a sheetbased on an image forming condition, the image forming apparatuscomprising: a passage configured to allow a sheet to be manuallyinserted thereinto; a reading sensor configured to read a surface of thesheet inserted into the passage; a display; and a controller configuredto: control the display to display a screen after reading a firstsurface of the sheet by the reading sensor, the screen being a screen tourge a user to read a second surface opposite to the first surface ofthe sheet; control the display to display a plurality of candidates of atype of the sheet based on a reading result of the first surface by thereading sensor and a reading result of the second surface by the readingsensor; and control the image forming conditions based on the type ofthe sheet selected from among the plurality of candidates displayed onthe display.
 9. The image forming apparatus according to claim 8,wherein the controller is configured to: perform a first mode and asecond mode, the first mode being a mode in which the controllercontrols the display to display the plurality of candidates for the typeof the sheet based on both the reading result of the first surface bythe reading sensor and the reading result of the second surface by thereading sensor, and the second mode being a mode in which the controllercontrols the display to display the plurality of candidates for the typeof the sheet based on the reading result of the first surface by thereading sensor; control, in the first mode, after reading the firstsurface of the sheet by the reading sensor, the display to display theimage.
 10. The image forming apparatus according to claim 9, wherein thecontroller is configured to: not display, in the second mode, afterreading the first surface of the sheet by the reading sensor, thescreen; and control the display to display the plurality of thecandidates for the type of the sheet based on the reading result of thefirst surface by the reading sensor.
 11. The image forming apparatusaccording to claim 9, wherein the controller is configured to: receiveuser instruction information to instruct to perform the first mode; andselect the first mode based on the user instruction information.
 12. Theimage forming apparatus according to claim 9, wherein the controller isconfigured to control the display to display a selection screen to allowthe user to select whether to perform the first mode after reading thefirst surface of the sheet by the reading sensor.
 13. The image formingapparatus according to claim 8, further comprising a sheet sensorconfigured to detect the sheet that has arrived at a detection positionon downstream of the reading sensor in an insertion direction in whichthe sheet is inserted, wherein the controller is configured to acquirethe reading result of the first surface that is read by the readingsensor after detecting the sheet by the sheet sensor.